The present invention relates in general to liquid, semi-liquid and thickened working substances which contain spirodiphosphates, and to spirodiphosphate-containing greases, lubricating oils, transmission, brake and hydraulic fluids in particular.
Working substances are materials which, in addition to whatever other functions they may perform in a given system, serve to reduce friction between moving parts in the system in which they are used. Accordingly, working substances include greases, such as those applied to bearings and universal joints, friction reducing lubricating oils for wet clutches, and extreme pressure cutting oils for metal working operations. Working substances also include transmission fluids, which reduce the wear of transmission parts in frictional contact, and hydraulic fluids, which often perform the dual function of lubricating the pump of the hydraulic system in which they are used.
Many factors, such as lubricity, viscosity and compatibility with system components, may be important in selecting a working substance for a particular application. However, it is particularly desirable that such compositions possess antioxidant properties, particularly at elevated temperatures, as oxidation of a working substance under the conditions of use may at least partially destroy its favorable properties, such as lubrication, with potentially serious attendant consequences.
Although a vast number of different working substances are known in the art, many of these compositions may not provide antioxidant or friction reducing characteristics which are adequate for the systems in which they are used.
Certain spirodiphosphate compounds are known in the art. Descriptions of spirodiphosphates may be found in U.S. Pat. No. 3,978,167 to Albright; U.S. Pat. No. 3,325,566 to Ratz; and U.S. Pat. No. 4,086,205 to Birum, as well as various portions of Chemical Abstracts. These compounds are disclosed as being useful as flame retardants, particularly for various polymer compositions, or as stabilizers or intumescent agents for various coatings such as paints.
Other phosphorus based compounds are known as additives for lubricant compositions. U.S. Pat. No. 3,192,243 to Gagliani discloses pentaerythritol diphosphite derivatives as additives to lubricating oils. These compounds are disclosed as principally functioning as antioxidants, due to the presence of the trivalent phosphite group.
U.S. Pat. No. 4,348,291 to Shim and U.S. Pat. No. 3,846,317 to Lintzenich disclose alkenyl phosphoramides and phosphoramides of triazoles, respectively, as extreme pressure additives. However, although phosphoramides may offer some improvement over other additives or the unmodified lubricant, phosphoramides may not perform as well as desired in certain applications.
Problems with inadequate performance of phosphoramides and other working substances may be particularly acute in certain applications, such as sealed universal joints, wherein replacement or replenishment of the working substance is difficult or impracticable and premature failure may result in damage to equipment. Therefore a working substance which exhibits improved antiwear or antioxidant properties offers significant practical advantages over many compositions known in the art.